Serial calculations of glomerular filtration rate were made in 31 pediatric liver transplant recipients surviving more than 1 year. GFR was computed from the Schwartz formula, (cGFR = KL/S Cr), before orthotopic liver transplantation, and at 3-6 monthly intervals thereafter. At the same time points, CsA dose/kg, CsA level, blood pressure, and liver functions were recorded. The mean difference between the pre-OLT cGFR and the most-current cGFR for all patients was -50 ml/min/1.73 m2 (P = less than 0.005). In 17/31 (55%), the current cGFR was less than 80 ml/min/1.73 m2, indicative of renal impairment. The cGFR continued to decrease in 24 patients followed beyond 1 year (26.8 ml/min/1.73 m2 per year decrease, P less than 0.005). More patients with a cGFR less than 80 ml/min/1.73 m2 had outpatient hypertension. There was no correlation of cGFR with CsA levels, CsA dose, or liver function. We conclude that a significant decrease in cGFR is seen in children treated with CsA for more than 1 year, which is progressive in the majority.